Correct logic but wrong term. There is no such thing as a 1st harmonic. There is the fundamental frequency, next comes the 2nd harmonic (an even harmonic), then the 3rd (an odd harmonic), etc.

I know it sounds wrong but harmonics are named starting with the 2nd

Lefty

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Measurement changes behavior

 

Actually you misread what he put, your quote clearly says "first ODD harmonic" - bit of a strange way to put it, but actually perfectly correct. Presumably English isn't his first language?.

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Hi,

I am working with a feedback circuit for a sensor. I excite the sensor with a sinesodal voltage of aroung 50-200mV and 1K-500KHz. The output of this sensor is to read and so it is amplified. Now I need to put back the output voltage to 50-200mV since it is a feedback. I tried to use an AGC for this purpose but turned out to be real complicated for low amplitude signals. So I thought of using an diode clamping circuit to serve my purpose. But this gives a square wave of different harmonics. I need to convert this to a sine wave to avoid this. Can you suggest me any circuitry to serve my purpose. Can you also suggest any simple circuitry for AGC if any. Kindly do this help.

Regards,
Deepika

 

Hi Hero999,

I do not know your name and I apologize for addressing you using your username. You were talking about an AGC circuit if you want the amplitude to vary less. Can you suggest me an simple AGC circuit with couple of opamps, resistors and capacitors. I really need an AGC which can control my amplitude in the range of 10-100mV.

Regards,
Deepika

 

hai to all. Any one have a circuit using LM324 Op-Amp to convert square wave to sine wave. please pa its very urgent.

 

Take a look here.
A Quick Sine Wave Generator

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Pay it forward.

 

im quite sure if there was a simple one it would have been posted in this thread already as its over a year old, mabey try some of the ideas suggested earlier

 

The lousy old LM324 has full output up to only 2kHz. It is low power without enough bias current in its output transistors so it has up to 3% crossover distortion.

Better opamps go up to at least 100kHz at full output without any measurable crossover distortion.

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Uncle $crooge

 

Hi Mike,

Ok, i did, and found that the design equations and even philosophy
isnt quite right. Let me explain...

First, a fixed frequency sine wave generator made from a square
wave generator followed by a filter (as that article is about) to
smooth the square wave into a sine wave is best by making
the filter a bandpass filter rather than a low pass filter. That
design uses a low pass filter so it's not as good as one that uses
a band pass filter, and since both designs use about the same
number of components, why not use a band pass instead?
The low pass does not produce as good a sine wave, with the
tops bent to the left somewhat instead of an almost pure sine.
It's not too bad i guess, but with the same components a
bandpass would be better.

Second, the design formula for the filter provides for a very
high output which allows too much of the original square
wave to reach the output. This leads me to believe that
the second formula:

R5=1/(8.8856*F*C1)
R6=R5

is also incorrect.
A better formula would be:

R5=2/(8.8856*F*C1)
R6=R5

which effectively doubles R5 and R6.


Third, the design formula for the center frequency of the
square wave oscillator is totally incorrect. This would result
in the calculation of components that dont provide the
correct operating frequency.
The formula given is:

R1=(0.5*F)/(0.693*C1)

but it's obvious with that oscillator that as frequency increases R1 has to
decrease, so the corrected formula is:

R1=(0.5)/(0.693*C1*F)


These formula changes make a better sine wave oscillator,
but again if the output filter was a BP type it would be
even better.

 

thank you mike bits. your circuit works very well. any do you any one have LEAD ACID BATTERY CHARGER WITH AUTO CUT OFF circuit.

 

where would i be able to find a schematic for a 220v 50hz true sine wave inverter?
I am looking for something large to use as a backup for my whole house....

Why are true sinewave inverters so scarce?

 

A true sinewave inverter has a very complicated circuit.
Use a gasoline-engine powered generator.

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Uncle $crooge

 

A gasoline-powered generator sounds the easiest solution. Be careful, power companies call this "back feeding", they can get nasty if they think there's a risk of power finding its way onto their network. Linesman have be killed this way.

probably because the power density of storage batteries is so low, compared to that of a fossil fuel powered generator. Also the capital outlay and maintenence for the equivalent energy in the form of storage batteries is a lot more expensive than a tank of diesel/gas.



While I'm here, I'll answer the orig posting of 2 years ago.....
1. Make the opamp into a sine wave oscillator. e.g. a "phase shift", "twin-T" or "wein bridge".

2. When you close the feeback loop, don't provide enough feedback for it to freely oscillate (just increase an R if it's a wein bridge).

3. Choose enough feedback for it to "ring" at the oscillator centre frequency.

4. Couple the square wave, to this 'oscillator'. Tight if you want a wider range of frequency, looser if you want lower distortion. The output will be in phase with the sq wave. You'll probably need AGC.

PS. Instead of opamp, if you used just a single transistor (eg as a 'phase-shift-oscillator'), the circuit will be lower parts count, and you'll probably get away without needing AGC (e.g. thermistor). Because a simple common emitter BJT circuit is non-linear and what is "nasty distortion" in audio design, is here a nice 'compression' function to stabilise the sine amplitude.
Hope this helps, I'd done this trick before and it worked for me. I used several of these to clean up a group of sinewave tones received over a radio link.